Time-resolved photoacoustic calorimetry is a technique developed in our laboratory that enables one to determine the dynamics of enthalpy and volume changes for photoinitiated reactions that generate either stable products or transient intermediates. The capabilities of the technique are such that the sum of enthalpies and volume changes can be measured for timescales less than 2.5 nsec. For reaction times ranging from 2.5 nsec to 20 microsec the dynamics and amplitudes of enthalpy and volume changes can be resolved. We proposed to examine the photoacoustic calorimetry of the visual protein rhodopsin. We will examine the time-resolved enthalpy and volume change profile for the bleaching sequence of rhodopsin in disk membranes from 2.5 nsec to 20 microsec. We will probe for the possible involvement of protons in the early chemistry of vision, investigate conformational changes in the protein that might serve to activate enzymes and elucidate the effect of lipids and detergents upon the chemistry of rhodopsin. The values obtained from the enthalpy and volume changes will be important new data for the development of models for the visual process as well as models for the dynamics of membrane bound proteins in general.